U.S. patent number 4,789,594 [Application Number 07/039,003] was granted by the patent office on 1988-12-06 for method of forming composite radius fillers.
This patent grant is currently assigned to The Boeing Company. Invention is credited to Stanley W. Stawski.
United States Patent |
4,789,594 |
Stawski |
December 6, 1988 |
Method of forming composite radius fillers
Abstract
A laminated board is built up from a plurality of layers of
composite material having substantially unidirectional fibers. The
layers are arranged so that all of the fibers in the board are
substantially parallel to the length of the board. The board is cut
at alternate 60.degree. angles with respect to a bottom layer of
the board in the direction of the fibers to form a plurality of
strips having a substantially triangular cross section. The strips
are then advanced through a rolling machine which forms radiused
surfaces on two adjacent sides of an equilateral triangle which is
described by the cross section of the strip. Tapered fillers are
formed by varying the thickness of the board from one end to the
other. A strip-cutting machine having an angled blade, guides for
the board, and a mechanism for translating the blade with respect
to the board is also disclosed.
Inventors: |
Stawski; Stanley W. (Pierce,
WA) |
Assignee: |
The Boeing Company (Seattle,
WA)
|
Family
ID: |
21903132 |
Appl.
No.: |
07/039,003 |
Filed: |
April 15, 1987 |
Current U.S.
Class: |
428/397; 156/222;
156/264; 156/269; 264/241; 428/902 |
Current CPC
Class: |
B26D
1/02 (20130101); B26D 7/0608 (20130101); B29C
70/28 (20130101); B29D 99/0003 (20130101); B29D
99/0014 (20130101); B29D 99/0053 (20130101); B29C
2793/00 (20130101); B29K 2105/101 (20130101); B29L
2031/26 (20130101); Y10S 428/902 (20130101); Y10T
156/1075 (20150115); Y10T 156/1044 (20150115); Y10T
428/2973 (20150115); Y10T 156/1084 (20150115) |
Current International
Class: |
B26D
1/02 (20060101); B29C 70/04 (20060101); B26D
1/01 (20060101); B26D 7/06 (20060101); B29C
70/28 (20060101); B29D 31/00 (20060101); B32B
001/04 () |
Field of
Search: |
;83/436,707,718,722
;156/222,250,269,264 ;244/123 ;264/241 ;428/397,902 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dawson; Robert A.
Attorney, Agent or Firm: Seed and Berry
Government Interests
STATEMENT OF GOVERNMENT INTEREST
The government has certain rights in this invention.
Claims
I claim:
1. A method for forming composite radius fillers of the type having
a desired cross-sectional shape, comprising the steps of:
building an elongated rectangular board having two ends from a
plurality of layers of composite material, wherein each layer has a
plurality of elongated fibers substantially aligned so as to be
substantially parallel and wherein substantially all of the fibers
in the board define a fiber direction aligned with the board
length;
separating elongated strips from the board in the fiber direction
so that the strips have an intermediate cross-sectional shape which
approximates the desired composite radius filler cross-sectional
shape; and
forming the elongated strips in a forming device to the desired
cross-sectional shape.
2. The method of claim 1 wherein the separating step includes a
step of cutting the elongated strips from the board in the fiber
direction with a cutting device.
3. The method of claim 2 wherein the elongated strips are cut at an
acute angle with respect to a bottom layer of the board.
4. The method of claim 3 wherein the cutting device is translated a
predetermined distance transverse to the fiber direction and
wherein the board is rotated end-for-end about an axis transverse
to the fiber direction before subsequent separating steps so that
the intermediate cross-sectional shape of the strips is
triangular.
5. The method of claim 4 wherein the acute angle is approximately
60.degree., whereby the intermediate cross-sectional shape is
approximately an equilateral triangle.
6. The method of claim 4 wherein the board has a thickness of
approximately 0.25".
7. The method of claim 4 wherein the board building step includes
using layers of composite materials having varying lengths and
positioning the layers so that the board has a tapering thickness
between the ends, whereby alternate elongated strips have
correspondingly tapered, triangular cross sections.
8. The method of claim 1 wherein the layers include sections of
composite tape having substantially unidirectional fibers
pre-impregnated with a binding agent wherein each layer has a
thickness of approximately 0.007" to 0.009".
9. The method of claim 1 wherein the board has a thickness of
approximately 0.25".
10. The method of claim 1 wherein the board has a width of
approximately 12".
11. Composite radius fillers for use in construction of composite
structural joints, made by the process comprising the following
steps:
building an elongated rectangular board having two ends from a
plurality of layers of composite material, wherein each layer has a
plurality of elongated fibers substantially aligned so as to be
substantially parallel and wherein substantially all of the fibers
in the board define a fiber direction aligned with the board
length;
separating elongated strips from the board in the fiber direction
so that the strips have an intermediate cross-sectional shape which
approximates the desired composite radius filler cross-sectional
shape; and
forming the elongated strips in a forming device to the desired
cross-sectional shape.
12. A method for forming composite radius fillers of the type
having a desired cross-sectional shape, comprising the steps
of:
building an elongated rectangular board having two ends from a
plurality of layers of composite material, wherein each layer has a
plurality of elongated fibers substantially aligned so as to be
substantially parallel and wherein substantially all of the fibers
in the board define a fiber direction aligned with the board
length; and
separating elongated strips from the board in the fiber direction
so that the strips have an intermediate cross-sectional shape which
approximates the desired composite radius filler cross-sectional
shape.
13. The method of claim 12 wherein the separating step includes a
step of cutting the elongated strips from the board in the fiber
direction with a cutting device.
14. The method of claim 13 wherein the elongated strips are cut at
an acute angle with respect to a bottom layer of the board.
15. The method of claim 14 wherein the cutting device is translated
a predetermined distance transverse to the fiber direction and
wherein the board is rotated end-for-end about an axis transverse
to the fiber direction before subsequent separating steps so that
the intermediate cross-sectional shape of the strips is triangular.
Description
TECHNICAL FIELD
The invention relates to radius fillers for composite structures.
More specifically, the invention relates to methods and apparatus
for forming radius fillers for use in junctions between sections of
composite structures.
BACKGROUND ART
Composite structures made from fibrous materials, such as
Fiberglas.RTM., graphite fibers and various resins, such as epoxy,
are finding increased use as substitutes for metal in aircraft and
other structures. It is well known that composite structural
elements can be specifically designed for various structural
purposes by selecting the appropriate filament direction and
laminate structure of the composite.
The use of composites in structural members such as I-beams and
flanges has presented a particular problem. It is known that the
junction between two perpendicular composite layers is prone to
peeling. U.S. Pat. No. 3,995,080, issued to Cogburn et al.,
describes the use of fillers (fillets) which are radiused to
conform to the junction between perpendicular composite structures,
such as the web and flange sections of an I-beam.
In U.S. Pat. No. 4,331,723 issued to Hamm and assigned to the
assignee of the present invention, the use of composite fillers is
described in conjunction with additional reinforcing structure.
Fillers of the type described above are generally triangular in
cross section. Two adjacent sides of the filler are radiused to
conform to curvature at the junction of the perpendicular composite
structures.
Formation of the fillers is a tedious, laborintensive, and
expensive procedure. The conventional method for forming fillers
includes a series of manual steps. In the first step, a section of
composite material which has been pre-impregnated with resin is
folded or rolled to form a roughly rectangular or cylindrical
shape. Where the filler is designed for use in an elongated
structural member such as an I-beam, the filler must be provided
with a length equal to the structural member; the filler may be a
few inches long, five feet long, six feet long, or longer. The
pre-impregnated composite tape is difficult to handle because it is
generally tacky at room temperature. It is very difficult to fold
this material into a rectangular or triangular cross section having
a width of approximately 1/4" because of the tackiness.
Furthermore, substantial nonuniformity in the folded material is
unavoidable.
After the composite material has been rolled or folded into an
elongated shape, the material is roll-formed in a second step by a
conventional roll-forming machine to produce the desired triangular
cross section with radii on two adjacent sides. Nonuniformities in
the folded material can jam the roll-forming machine.
Therefore, a need exists for a simplified, economical method of
forming radius fillers for composite structures.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a method for
forming composite radius fillers having uniform dimensions.
It is also an object of the present invention to provide a method
for forming composite radius fillers efficiently and
inexpensively.
It is yet another object of the present invention to provide a
method for forming tapered radius fillers.
It is still another object of the present invention to provide an
apparatus for forming composite structure radius fillers.
The invention achieves these objects, and other objects and
advantages which will become apparent from the description which
follows, by providing a method for forming composite radius fillers
having a substantially parallel fiber direction. In a first step,
an elongated board is constructed from a plurality of layers of
composite material. Each layer has a plurality of elongated fibers
which are aligned substantially parallel to one another and to the
length of the board. In a second step, elongated strips are
separated from the board in the fiber direction. The strips are
easily separated from the board because the fibers are
substantially parallel to one another and to the length of the
board. The strips are separated from the board so that each strip
has an intermediate cross-sectional shape which approximates the
ultimate desired cross-sectional shape of the radius filler. In a
third step, the elongated strips are then formed in a forming
device to achieve the desired cross-sectional shape. It is also
possible to use the elongated strips as radius fillers without
forming the elongated strips in the third step.
In the preferred embodiment, the elongated strips are separated
from the board during cutting steps. The strips are cut at an acute
angle with respect to a bottom layer of the board. Between each
cutting step, the board is rotated about a transverse axis
end-for-end and the cutting blade is translated a predetermined
distance so that the resulting strips have an intermediate
cross-sectional shape which approximates an equilateral triangle.
The strips may then advance through a conventional roll forming
machine to achieve the desired radius shape on two adjacent sides
of each strip.
Tapered radius fillers are prepared by laying up a composite board
having layers of varying lengths. The layers are positioned so that
the board has a tapered thickness between the ends thereof. In this
way, every other strip separated from the board has a
correspondingly tapered, triangular cross section.
An apparatus for forming the composite radius fillers of the
present invention is also disclosed. The apparatus has an elongated
table which has a table surface for supporting the board. A cutting
blade is disposed on the table surface at an acute angle thereto.
The blade slides transversely with respect to the table surface.
Guides are provided to guide the board toward the blade in a
direction parallel to the fiber direction of the board. Prior to
cutting each filler from the board, the blade is translated and the
board is rotated about a transverse axis end-for-end so that the
resulting fillers have an equilateral, triangular cross section. A
drive mechanism can be provided to automatically drive the board
through the cutting blade.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial isometric view of a laminated board in
accordance with the present invention.
FIG. 2 is an enlarged, partial isometric view of a section of the
board indicated by the circled area in FIG. 1.
FIG. 3 is an isometric view of a strip-cutting machine in
accordance with the present invention.
FIG. 4 is an enlarged isometric view of a blade carriage used in
the apparatus shown in FIG. 3, and a schematic representation of
cuts made by the blade in the composite board.
FIG. 5 is a schematic representation of a conventional roll-forming
machine.
FIG. 6 is an enlarged sectional view taken along line 6--6 of FIG.
5.
FIG. 7 is an enlarged sectional view taken along line 7--7 of FIG.
5.
FIG. 8 is a schematic representation of a composite I-beam
illustrating the position of composite radius fillers produced by
the method and apparatus of the present invention.
FIG. 9 is a schematic representation of a composite board for the
production of tapered fillers in accordance with the present
invention.
FIG. 10 is an enlarged isometric view of a waste strip produced
from the board shown in FIG. 9.
FIG. 11 is an enlarged isometric view of a tapered strip produced
from the board shown in FIG. 9.
FIG. 12 is a sectional view taken along line 12--12 of FIG. 10 of
the waste strip.
FIG. 13 is an enlarged sectional view taken along line 13--13 of
the tapered strip shown in FIG. 11.
BEST MODE FOR CARRYING OUT THE INVENTION
A composite board for the production of tapered fillers in
accordance with the present invention is generally indicated at
reference numeral 20 in FIG. 1. The board is made up from a
plurality of layers 22 of composite material. The board has a right
side 24, an opposite left side 25 (see FIG. 3), a first end 26, a
second end 28, a top layer 30, and a bottom layer 32. The board is
generally rectangular.
As best seen in FIG. 2, each of the layers 22 consists of a
plurality of substantially unidirectional fibers 36. The layers are
pre-impregnated with a resin or other binding material, as
generally represented by droplets 38.
In this preferred embodiment, the layers 22 are sections of
resin-pre-impregnated composite tape which are layered and pressed
to form the composite board 20. The tape has a width of
approximately 3", 6" or 12" and a thickness of approximately 0.007"
to 0.009". The tape is generally supplied with a backing (not
shown) which is removed before the layers are applied to one
another. The resin is generally tacky or sticky at room
temperature; thus the layers adhere to one another so as to form
the board. It is important that the layers be assembled so that the
unidirectional fibers 36 of each layer are substantially parallel
to one another and parallel to the left and right sides of the
board 30. This provides a composite board 20 which can easily be
split by a force applied in a direction parallel to the fiber
direction.
A strip-cutting machine which cuts strips from the composite board
20 is generally indicated at reference numeral 50 in FIG. 3. The
machine has a frame 52 which supports a table surface 54. The
machine also has a guide mechanism 56, a blade carriage 58, a pair
of idler rollers 60, 61, and a drive suspension 62. The drive
suspension 62 has drive rollers 64, 65 and a drive system generally
indicated at reference numeral 66. The drive rollers 64, 65 are
knurled or otherwise provided with a surface having a high
coefficient of friction.
The guide mechanism 56 is connected to the table surface 54 and
serves to direct the board 20 in a cutting direction 70 which is
parallel to the orientation of the unidirectional fibers 36.
The blade carriage 58 supports a blade 72 having a cutting edge 74.
The blade is preferably thin. A conventional utility knife blade is
suitable for this purpose. The blade carriage is slidably engaged
with a track 76 on the table surface 54 so that the cutting edge 74
is translatable with respect to the board 20 in a direction which
is transverse to the orientation of the unidirectional fibers 36.
The track 76 engages a track slot 78 in the blade carriage. The
carriage has an aperture 80 sufficient to accept the board 20
therein.
The blade is disposed at a 60.degree. angle with respect to the
table surface. Setscrews 82 threadedly engage a blade-retaining
block 84 to secure the blade 72 within the blade carriage 58. The
blade edge 74 separates the board 20 into elongated strips having
triangular cross-sections, as indicated by dotted lines 86 in FIG.
4. The plane of the blade 72 is substantially parallel to the
orientation of the unidirectional fibers 36. Therefore, individual
fillers are easily separated from the board by the blade. It is
important that the board be separated into individual strips and
then formed into fillers before the board is cured. The strips are
easily separated from the board as long as the board is
uncured.
The following method is used to separate individual fillers from
the board. The board 20 is inserted into the guide mechanism 56 as
shown in FIG. 3. The board is manually advanced until the second
end 28 of the board 20 is grasped between the drive roller 64 and
idler roller 60. The drive system 66 advances the board to the
blade carriage 58. The blade carriage is positioned in a right-hand
position, as shown in FIG. 3. The first cut made by the blade is
indicated by dotted line 88 (note that an initial cut 89 to remove
a waste piece 90 has been completed). The board 20 is advanced
through the blade 72 and is grasped by the drive roller 65 and
idler roller 61. After the first end 26 of the board has passed
through the drive roller 64 and idler roller 60, the drive roller
65 and idler roller 61 pull the remainder of the board through the
blade. Completion of the cut indicated by dotted line 88 produces
an elongated strip 92 (see FIG. 5) which has an intermediate
cross-sectional shape 94, shown in FIG. 6.
To achieve the desired cross-sectional shape 96 shown in FIG. 7,
the strip 92 can be formed by a conventional roll-forming machine,
schematically illustrated at reference numeral 100. A suitable
roll-forming machine is described in U.S. Pat. No. 4,559,005,
issued to Gants et al. The strip 92 is readily formed into the
shape 96, having two radiused adjacent sides 110, 112, by an upper
roller 114 which has correspondingly radiused surfaces 116. A lower
roller 118 has a flat circumferential surface 120 to supply a
reaction force against the bottom 122 of the strip 92. It has been
found that the uniform shape of elongated strips 92 produced by the
method described above substantially reduces jamming in the
roll-forming machine 100 over conventional prior art techniques. In
certain applications, the elongated strips may be used as fillers
without being formed in the roll-forming machine.
FIG. 8 illustrates a composite I-beam, generally indicated at
reference numeral 130, which utilizes composite radius fillers 132
of the present invention. The beam has an upper flange 134 which is
connected to a substantially parallel lower flange 136 by a
perpendicular web 138. The web 138 includes two adjacent sections
140, 141 which are laminated to the upper and lower flanges 134,
136. The radiused fillers 132 fill a void which would otherwise
occur at the junction of these parts and lend substantially
increased peel resistance to the structure. The flanges, adjacent
web sections, and fillers are simultaneously cured to form a
unitary structure. The fillers 132 can also be used at the junction
of plies on "T" sections, flanges, and other composite
structures.
In order to form each subsequent elongated strip from the board 20,
the blade carriage 58 is translated to the left a predetermined
distance equal to one-half the desired width of the filler 132. The
board 20 is then rotated about an axis transverse to the
orientation of the unidirectional fibers 36 end-for-end so that the
end 28 of the board is adjacent to the drive roll 64 and idler roll
60. As is described below, the guide mechanism 56 is adjusted to
re-center the board 20 on the table surface 54. Advancing board in
the cutting direction 70 will therefore produce a cut indicated by
dotted line 150. After this second elongated strip is completely
separated from the board 20, the board is again rotated end-for-end
and advanced through the strip-cutting machine 50 to produce the
next elongated strip.
To maintain the board 20 in a centered position on the table 54,
the guide mechanism 56 is provided with movable guides 156, 157.
The guides can be constructed from any suitable low-friction
material or can be provided with a low-friction coating, such as
Teflon.RTM. brand coating. The guide 156 has a threaded flange 160
which protrudes from a slot 162 in the guide mechanism 156. The
guide 157 is provided with a threaded flange 164 which also
protrudes through the slot 162. The flanges 160, 164 are
counter-threaded so that a threaded shaft 166 which has
correspondingly counter-threaded left- and right-hand halves causes
the guides to move apart or move together upon rotation of a knob
168. As previously described, the knob 168 is adjusted after each
elongated strip 92 is removed from the board 20 to maintain the
central position of the board with respect to the table 54.
Inserts (not shown) may be provided which are retained in the
guides to closely receive the sides of the board 20. Note that
before the first waste piece 89 is removed, the sides 24, 25 of the
board are substantially perpendicular to the table 54. If the
guides 156, 157 are provided with vertical interior surfaces which
are perpendicular to the table 54, the guides 156, 157 will
adequately receive the board 20. However, after the first waste
piece 89 is removed, the right side 24 of the board will form a
60.degree. angle with the table surface 54. Therefore, it is
preferred that an insert be provided for the guide 157 which has a
correspondingly angled surface. The insert may be provided with an
end flange which overlies a portion of the guide 157 to prevent the
insert from sliding in the cutting direction 70 with the board
20.
The drive suspension 62 of the strip-cutting machine 50 is provided
with a spring-biasing mechanism 170 which pivots the drive
suspension 62 about a drive system axle 172. Rotation of a knob 174
applies spring compression to squeeze the board 20 between the
drive roller 64 and idler roller 60. The driver roller 65 is
provided with a separate, independent spring-bias mechanism 176
which squeezes the board 20 between the drive roller 65 and idler
roller 61. Adjustment of the separate spring-bias mechanism 176 is
achieved by rotation of control knobs 178.
The strip-cutting machine 50 is also suitable for forming tapered
elongated strips 180, as shown in FIG. 11. A modified composite
board, generally indicated at reference numeral 182, is advanced
through the machine to produce the tapered elongated strips. The
modified composite board 182 tapers in thickness from a first end
184 to a second end 186. The method of constructing the board 182
is similar to the method of constructing composite board 20, except
that individual layers 188 are formed from sections of composite
tape have different lengths. Individual layers are arranged so that
each layer has one end at the first end 184 of the board 182 and
the other end at regularly spaced intervals toward the second end
186 of the board. As an example, the thickness of the board at the
first end could be 1/2", whereas the thickness of the board at the
second end could be 1/4", with a smooth taper in-between. The width
and length of the board are constant.
The modified composite board 182 is advanced through the
strip-cutting machine 50 as previously described for the composite
board 20. Note that the first piece 190 cut from the modified board
182 will be a waste piece, as was waste piece 89. However, the next
piece 192 will also be a waste piece because the second end 186
(see FIG. 10) will have a truncated vertex 194. Upon reflection, it
will become apparent that the next subsequent piece 196 will have a
pointed vertex, as shown in FIGS. 11 and 13. All of the tapered
strips in FIG. 9 which have their vertices pointing downward will
have the cross-sectional shape shown in FIGS. 11 and 13 and thus
will be usable for tapered fillers. All of the strips having
vertices at first end 184, which point upward, will be waste
pieces, because the vertices at the second end 186 will be
truncated and not usable. The tapered strips shown in FIGS. 11 and
13 are difficult to roll-form in the conventional manner because of
their non-constant cross-sectional shape. Therefore, the tapered
strips are preferably used as tapered radius fillers directly,
without any subsequent forming step.
Other variations of the invention described above are contemplated.
For example, rather than rotating the board 20 about a transverse
axis end-for-end to produce the desired strip cross-sectional
shape, the blade 72 can be rotated about an axis parallel to the
table surface 54 so that the blade position defines the opposite
side of the equilateral triangle. Therefore, the invention is not
to be limited by the above description, but is to be determined in
scope by the claims which follow.
* * * * *